In general, pressure-sensitive adhesive (PSA) exists as a soft solid (a viscoelastic material) in a room temperature range and has a property to adhere easily to an adherend with some pressure applied. Taking advantage of such a property, PSA has been widely used as a means of attachment that offers excellent workability and produces dependable adhesion in various industrial fields from home appliances to automobiles, OA equipment, and so on. As the base polymer of PSA, a polymer that exhibits rubber elasticity at room temperature can be preferably used. Technical literatures related to PSA include Patent Documents 1 and 2. Patent Document 1 discloses a light-curable acrylic PSA. Patent Document 2 relates to a PSA sheet using a polyolefinic foam substrate which is non-viscoelastic.